Motor vehicles with hybrid drive are known in which a drive axle is driven by an internal combustion engine, while another drive axle can be driven by an electric motor. The motor vehicle is not normally driven permanently by the electric motor but selectively, and adapted to the driving situation. Typically, the electric motor drive is engaged under acceleration, in particular from a standstill, when climbing and in particularly dynamic driving situations, whereas at continuous speed the motor vehicle is driven substantially by the internal combustion engine. The correspondingly adapted, selective addition of an electric motor drive as a whole allows an increase in efficiency of the drive.
In order to couple an electric motor, as a drive of a motor vehicle with hybrid drive, with the drive axle to be driven thereby, or to separate this from the drive axle, clutches can be used which selectively transmit torque output by the electric motor to the drive axle. These are usually positive-locking clutches in which an input-side clutch element and an output-side clutch element intermesh via toothings. When such a clutch is closed, for friction-free operation it must be ensured that a possible tooth-to-tooth positioning of the toothings to be connected can be overcome by a suitable mechanism. When the clutch is opened during driving, when therefore the toothings of the coupled clutch elements intermesh, the difficulty arises that the torques transmitted between the clutch elements must prevent mutual separation of the clutch elements and that therefore a correspondingly high force must be applied.
Clutches for selective separation of an electric motor from a drive axle of a motor vehicle may for example be electromechanical in type, i.e. the clutch has its own electric motor with reduction gear mechanism which can be operated as an actuator to adjust the clutch. With corresponding configuration, the power of such an electric motor is sufficient to move the clutch from the closed to the open state even under substantial torques transmitted between the clutch elements. However such a design of a clutch requires a relatively large construction space and also has a high power requirement.
Clutches are also known which are moveable by electromagnetic actuators. In a hybrid drive of the type described, such clutches can be arranged on the output side of a gear mechanism active between the electric motor and the drive axle. This however has the consequence that the capacity of the clutch must be designed for the possibly high torque values which can occur at the drive axle.